Water jet blasting and abrasive water jet machining
The principle of water jet machining consists of the projection of a flow of water at a pressure greater than 410 MPa that is passed through a hole, whose diameter ranges between 0.8 mm and 7.6 mm, to form the pressure jet that produces the cutting of the material.
Furthermore, in the abrasive water jet projection cutting method, an abrasive material is included in the fluid that is introduced into the water flow through a mixing chamber, and from there it is passed to the nozzle where it is accelerated and projected together with the fluid on the material to be cut. The size of the abrasive will determine the final finish of the piece.
This process has both positive and negative aspects:.
laser machining
Laser machining for polymer matrix composite materials consists of a high-energy cutting system where at no time is contact established between the mechanism and the piece, so cutting forces are not generated and the material clamping system can be simple. This type of machining allows cutting a wide range of composite materials, being especially effective for making complex cutting shapes.
The laser beam equipment concentrates all the energy at one point using a lens system. This reduces the diameter of the beam, allowing highly precise machining (cutting lengths less than 0.1 mm) to be achieved.
Laser cutting is usually accompanied by a gas flow that eliminates excess material and protects the focusing lenses. The gas used to machine composite materials is air, since there is no risk of oxidation as occurs in metals, where inert gases such as argon are usually used.
Ultrasonic machining
The ultrasonic machining system is based on the use of a blade that vibrates at ultrasonic frequencies (around 20,000 Hz), and cutting speeds of up to 1000 mm/s can be achieved.
The equipment used for ultrasonic machining consists of the following main components:.
The minimum cutting tolerances obtained with this system are +/- 0.0125 mm, and the maximum cutting depths are 25 mm for carbon fiber, glass and aramid laminates.
Electrochemical spark machining
Electrochemical spark machining is a process analogous to electroerosion, but it allows machining materials that are not metallic in nature, making it especially useful for laminates of composite materials.
The process takes place in a tank filled with an electrolyte which can be an aqueous solution of NaCl or NaOH. We have an anode and a cathode. The cathode will be the machining tool, and can be of two types: a shaped electrode, or a wire electrode.
When applying an electric current, sparks are produced on the surface of the cathode that will carry out the machining process, bringing the part closer to said tool, and keeping it at a fixed distance from the anode (50 mm). Maintaining the correct distances between the anode and the cathode, and between the part and the tool (cathode) is essential for the process to be successful.
As the voltage is increased, greater discharge energy is generated, a greater speed of spark formation and therefore a greater grinding ratio.
The shaped electrode is used to make a cavity or through hole in the material. The electrode or die will have the shape of the cavity to be made, and machining will occur through a relative vertical movement between the piece and the tool.
The wire electrode is based on the same idea as the previous one, but with the difference that now it is a wire that makes the cut, being able to describe complex trajectories. The quality, material and diameter of the wire, in conjunction with the voltage and amperage applied, are factors that directly influence the speed with which the part can be machined. Thread tension is another important factor in this process to produce an effective cut; In this way, a low tension will produce a poor finish on the piece, while an overtension can cause the thread to break at an unwanted moment.